The space at the top of your e-mail message is some of your most valuable real estate. Yet, many marketers fail to maximize their top-line content with ineffective navigation and lack of a useful preheader.

A strong preheader delivers key information for readers who can’t or don’t enable images, while navigation helps them move either down into the message or bypass the message and visit the areas of your website that interest them more.

Here’s how to make sure the preheader and your navigation (whether using inline navigation links or message design) work together to pull readers into the message.

Begin With the Preheader

Start with these tips for effective preheaders:

Don’t load up the preheader with line after line of administrative copy beyond your on-boarding series. While it makes sense to include a “View Online/View Mobile version” link as a secondary preheader, subscribers can ignore the add-to-address-book request if they do it right after they opt in or decide never to do it. Move administrative copy to your e-mail footer, and reserve the preheader for more powerful messages.

Be succinct. Some preheaders extend over two or three lines. While this does add content, it also comes close to overkill. Keep your promotional preheader to a single line for maximum impact.

This extends to the view online/view mobile copy. Wordy directions such as “If you are having trouble viewing this e-mail, click here to see it online” just take up space. Say “View Online” or “View Mobile,” and hyperlink them.

Don’t repeat your subject line. This doesn’t help the reader answer the three questions that will decide whether she opens your message, reads and acts on it, or deletes it:

Who is this message from?

What’s in it for me?

What do you want me to do?

Your sender address, subject line, and preheader work as a team to help answer these questions. One or two shouldn’t do all the work.

Make the preheader easy to read. Use a standard font size (minimum 8-point type size) in a readable color (basic black always works). Boldface the call to action to help draw the eye, and underline the link. It seems basic, but underlines still signal that content is clickable.

Don’t put forward-to-a-friend or share-with-your-network links in the preheader unless testing supports this placement. Why would recipients share your content if they haven’t seen what the message says or even decided yet what they want to do with it? Testing will tell you whether your sharing links will get the most visibility and action at the top, the bottom, or inside the copy itself. (More on navigation in the section below.)

Use the left and right content regions for different preheader goals. Left-justify your marketing preheader (the one with the call to action, secondary offer, etc.). This way, it will show up in both horizontal and vertical preview panes or on small mobile screens.

Include the coupon code. This makes it easy for the discount to show up in the shopping cart and to help shoppers find it quickly for copying and pasting on the order form if clicking through from the e-mail doesn’t automatically add the code.

Include deadlines for urgency. Not everyone opens your e-mail and shops on the day it arrives. Emphasize the end date by adding it to the preheader.

When promoting a limited-time offer, your subject line could say “Three-day Sale” and your preheader could begin “Ends 5/21/2010.”

Test everything, including navigation. Test various preheader configurations – design, placement, copy, links – before committing one to your template. Go against conventional wisdom, like adding the unsubscribe link to the preheader in addition to the administrative footer, but don’t make it a permanent template change until you test it.

Include your top-level navigation with your preheader testing, because the two can work together or against each other. Some elements that have always been fairly hidden in a bottom navigation bar will get better results for you at the very top in a preheader, but only testing can tell you that.

Study where recipients are clicking on your messages. A navigation link that draws few clicks should get reassigned elsewhere in the message. In its place, test navigation items that drive to deeper categories and resonate with the central call to action.

Conversely, clicks can also point you to new opportunities, both for refining your message navigation and in your e-mail marketing program itself. A low-lying link that draws disproportionate clicks can get moved up higher, making your e-mail more relevant to your recipients.

Suppose one of your most popular links is “New Products.” You can use that information to create a new, behavior-driven segment of your mailing list with recipients who are more interested in what’s new than in your regular weekly offer.